1. Field of the Invention
The present invention relates to a fixing roller of the general type used in the fixing part of an electrophotographic copier, laser printer, facsimile machine, etc.
2. Description of Related Art
The electrophotographic process generally includes a step in which a light-sensitive body is exposed to an image to form an electrostatic latent image on the light-sensitive body. Then, a colored charged particles toner powder is made to adhere to this electrostatic latent image so as to develop the image. The toner image is then transferred onto a piece of copy paper (sheet-like transfer material or recording material) in an un-fixed state. Finally, the unfixed toner image is fixed onto the copy paper by a method such as heating.
With regard to the fixing method, there are various methods such as heat roller fixing, fixing by the oven method (using the radiated heat of the heater), and pressure fixing. Among these, the most often-used fixing method in recent years is the heat roller fixing method wherein a pair of rollers internally provided with heating sources such as electric heaters and having their outer surfaces coated with rubber or resin of excellent releasability are urged against each other, and copy paper carrying a toner image formed thereon is passed between these rollers so that the toner image is fused onto transfer paper. In this case, a heating source may be provided in only one of the rollers so that the one roller is used as a heat fixing roller, while the other is used as a pressing roller.
Compared to other fixing methods, the heat roller fixing method has a very high thermal efficiency, and is suited to high speed operations, but it has a defect that the life of the heat roller is short.
Ordinarily, a fixing roller is configured so that an elastic layer and a resin layer are provided for purposes of offset prevention on the outer surface of a metallic roller (core) which is formed by metal such as stainless steel or aluminum. Conventionally, as an improved fixing roller, Japanese Patent Post-examination Publication No. Hei-1-24311,for example, proposes a fixing roller with a configuration where the outer surface of the metal roller is coated with an elastic layer consisting of fluororubber or silicone rubber, and, further, a layer consisting of fluororesin on top of this elastic layer. With regard to this fixing roller, not only is it superior in terms of the non-stickiness of the surface, but also abrasion or injury of the fluororesin layer is inhibited in the case where a paper guide contacts the rotating rollers, since the elastic layer is deformed via the thinly coated fluororesin layer, and since the fluororesin layer is also deformed along this elastic material.
Yet, with regard to the conventional fixing roller, peeling tends to occur between the elastic layer and the fluororesin layer with prolonged use, and durability is inadequate. In particular, since the combination of an elastic layer consisting of silicone rubber and a release layer consisting of fluororesin exhibits poor adhesiveness between the two, surface peeling easily occurs.
With regard to a fixing roller where a resin layer is formed on top of an elastic layer, a proposal is made in Japanese Patent Unexamined Publication No. Hei-1-147576according to which several holes are formed in the surface of the elastic layer which constitutes the boundary of the elastic layer and resin layer, and the resin layer is secured by an anchor effect due to the entry of the resin material into the pertinent holes. With regard to this method, a layer of silicone rubber mixed with quartz powder, for example, is provided on the outer surface of the metal roller and is vulcanized and molded, after which the quartz powder projecting from the elastic layer surface is removed by abrasive cloth and numerous holes are formed; a fluororesin layer is subsequently provided on top of this. Yet, since the silicone rubber forming the elastic layer and the fluororesin forming the resin layer have good mutual separability, the adhesive strength is weak, and with this type of physical retention means alone, there is danger of peeling at the junction part during use, and durability is still inadequate.